Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $248.34   13.816%   $282.6507   $282.65   $282.65   $282.70  
  Purchase #2 $238.28   13.223%   $269.7878   $269.79   $269.80   $269.80  
  Purchase #3 $68.91   6.408%   $73.3258   $73.33   $73.35   $73.30  
  Purchase #4 $102.53   5.654%   $108.327   $108.33   $108.35   $108.30  
  Purchase #5 $95.53   7.428%   $102.626   $102.63   $102.65   $102.60  
  Purchase #6 $200.69   8.584%   $217.9172   $217.92   $217.90   $217.90  
  Purchase #7 $37.89   12.463%   $42.6122   $42.61   $42.60   $42.60  
  7 purchase totals = $992.17       $1,097.2467   $1,097.26   $1,097.30   $1,097.20